1. Field of the Invention
The present invention relates to digital data storage, and more particularly, to a method of reducing the effect of vibration in a disk drive by adaptively adjusting the gain applied to an acceleration sensor signal.
2. Description of the Prior Art
A hard disk drive generally uses a transducer or xe2x80x9cheadxe2x80x9d located at the end of a rotary actuator to read and write data on a surface of a rotating disk having a magnetic media layer. The rotary actuator may exhibit an effective imbalance that is affected by linear vibrations experienced by the disk drive. Such vibrations may disrupt a track following operation in which a servo control system within the disk drive uses servo control information on the magnetic surface to hold the transducer at a desired track.
Accordingly, there exists a need for a technique for reducing the effect of vibration on a disk having an actuator exhibiting an imbalance during a track following operation. The present invention satisfies these needs.
The present invention may be embodied in a method, implemented in a disk drive, for adaptively reducing an effect of vibration during a track following operation. The disk drive has a head disk assembly (HDA) including a disk, rotary actuator, a transducer, and a voice coil motor (VCM) circuit. The disk rotates and has a surface coated with a layer of magnetic media. The disk includes distributed position information in a plurality of servo wedges for defining a plurality of concentric data tracks. The rotary actuator pivots relative to a base and has the transducer that periodically reads the position information from the servo wedges. The rotary actuator is coupled to the voice coil motor (VCM) circuit that includes a voice coil motor. The VCM circuit responds to a control effort signal that is periodically adjusted during a track-following operation based on the position information such that the transducer tends to follow a selected track.
In the method, a sensor signal is generated that is responsive to a vibration to the disk drive that tends to cause the rotary actuator to move off-track. The position information is read from a current servo wedge to generate a measured position signal. A nominal position error signal is generated based on a difference between the measured position signal and a target position signal. The sensor signal is read to generate a sensor value associated with the current servo wedge. The sensor value is modified based on a first adaptive-filter gain to generate a position error adjustment signal. The nominal position error signal is adjusted using the position error adjustment signal to generate an adjusted position error signal. A control effort signal is calculated based on the adjusted position error signal, and is output to the VCM circuit. The first adaptive-filter gain is then altered based on the adjusted position error signal and the sensor value associated with the current servo wedge for use during a next servo wedge.
In more detailed features of the invention, the first adaptive-filter gain may be altered for use by the next servo wedge by setting an adaptive filter. The adaptive filter may have one coefficient, or it may have multiple coefficients. The sensor value may be modified by multiplying the sensor value by the first adaptive-filter gain. The nominal position error signal may be adjusted by adding the position error adjustment signal to the nominal position error signal. The rotary actuator may exhibit an effective imbalance that may be affected by a linear vibration.
In other more detailed features of the invention, the control effort signal may be calculated by calculating a nominal control effort signal using the adjusted position error signal, modifying the sensor value based on a second adaptive-filter gain to generate a control effort adjustment signal, and adjusting the nominal control effort signal with the control effort adjustment signal to generate an adjusted control effort signal. The adjusted control effort signal may be output to the VCM circuit. The second adaptive-filter gain then may be altered based on the adjusted position error signal and the sensor value associated with the current servo wedge for use during a next servo wedge. The second adaptive-filter gain may be altered for use during a next servo wedge by setting a second adaptive filter.